here’s a movement right now for fitting the right engine in the right car — a MkI Cortina with a

Pre-Crossflow or indeed a 105E Anglia with the same, and there are plenty more examples, too... But with these ’60s Fords it always has been the logical step to go straight for a bigger capacity unit like the Crossflow — they’re 1600cc for starters and they virtually bolt straight in.

You could argue that a Kent engine is a Kent engine whether in Crossflow or Pre-Crossflow form, but if you’re after period correctness then the later engine doesn’t really look right. The issue is, if you want lots of performance, the Pre-Crossflow’s maximum standard capacity is a

T mere 1498cc, or 1558cc if you use a Lotus configuration. You can get these engines to perform, but it’s far easier with more capacity in the first place.

The Crossflow block has the potential for more — the standard practice now is a plus 0.090 inch overbore resulting in a 1700 (actually 1688cc). But there is greater power waiting if you use the right base — the South African-made AX block has the potential for 2-litres if you want a challenge.

Period correctWhat can you do if you want to keep your ’60s Ford looking, well, ’60s? On the faced of it, the two series of engine are extremely similar — they’re both Kents so why can’t

you simply bolt a Pre-Crossflow head on Crossflow bottom end? Well, there are widely-known fundamental differences — like the combustion chamber being in the piston in the later engine and therefore has a corresponding flat-faced head.

Combining the two isn’t difficult, though with the scarcity of original parts there are a few challenges. We take a look at the practical and traditional methods of a big-block Pre-Crossflow with Joe Allenby-Byrne at Throbnozzle Engineering.

You needn’t compromise power for looks anymore. With the right parts, a Pre-Crossflow can be turned into a lovely-revving Kent that will equal its later brother, even with a similar spec!

Contact Throbnozzle Engineeering

07724 000320 www.throbnozzle- racing.co.uk

Info

Hybrid Pre-CrossflowBuild it

Want a hot ‘60s Ford for the street but with a bigger-capacity motor that still looks like the original? Here’s what you need to know.Words and photos Jon Hill

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he Crossflow is an update of the previous Kent with a 3/8 inch (9.5 mm) taller deck height to accommodate the longer stroke and taller piston. The cylinder head and piston

configuration are also completely different — the Crossflow famously has its combustion chamber in the bowl of the piston — conforming to the Heron Principal, while the corresponding cylinder head is completely flat.

It’s worth noting that early Crossflow engines did have a small combustion chamber and a reduced size bowl in the piston too. These latter components have been used in Pre and Crossflow conversions but the piston crowns have needed machining to suit.

The Pre-Crossflow then, has flat-top pistons and the combustion chamber is in the cylinder head - these vary according to capacity and engine specification (low and high compression and GT versions). The gudgeon pins that fit the small end of the connecting rod into the underside of the piston are all the same size and format, plus the standard bore size is the same - therefore, on the face of it, it’s a simple job of swapping the Crossflow piston for the other and using the corresponding Pre-Crossflow head. But as we’ll see in a second, it’s not that simple.

From a practical point of view, the Pre-Crossflow, with its shorter stroke, is a better revving engine and one reason is the weight of the piston. These can be extremely heavy in the later Crossflow unit since it has to carry that combustion chamber and so is deeper.

There have been examples of large capacity standard-blocked Pre-Crossflows, however — the obvious increase used to be from the standard 80.97 mm bore to the Lotus of 82.55 mm, although you can go to 83 mm or 83.5 mm in nearly all blocks. For any bigger, ideally you’d need an L-block and/or liners. The maximum possible capacity then is 1650cc using an 85 mm bore and a 72.75 mm (Pre-Crossflow stroke) crank. The problem with a shorter height block is that you can only effectively increase stroked capacity even further with a more acute rod angle. This actually reduces the rpm potential and in extreme cases increases the propensity for the rod to be pushed out the side of the block, since the rod is in effect being directed sideways rather than down. The ideal cost-effective route then, is to build a hybrid using the Crossflow block.

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BLOCK CHOICE

Can you use any 1600 Crossflow block? On the face of it, yes but the preferred choice is the 711M version. These have big square mains caps, are physically fatter (shown up in a 10 mm increase across the engine mount bosses), plus this later version has larger cam followers — 13 mm (33/64 inch) compared with 11 mm (7/16 inch).

Earlier blocks though aren’t exactly weak and can be used since the 711M is getting scarce - everyone wants one so the price is at a premium. Early Crossflow blocks carried the casting marks 2737E although there’s an almost identical 681F too (albeit slightly later). In sequence, the 691M followed with square end caps, but it still has the smaller followers, which aren’t a problem if correctly run in with appropriate valve springs.

The block you need to watch though is the 771M, used in the MkI Fiesta, which carries no side engine mount bosses and is generally shorter overall.

So apart from the front-wheel-drive 771M block, all 1600 cranks and rods are basically the same and can be used in this conversion.

Crossflow vs Pre-CrossflowThe fundamental differences

64 January 2013

There are plenty of ways to build a hybrid Pre-Crossflow engine, but the natural choice is to use standard components — Pre-Crossflow pistons attached to Crossflow rods. Since the standard 1500 and 1600 bore sizes (and their oversize options) match at 80.97 mm, swapping the two is not that difficult.

But unless you’ve got a 1500 donor engine with good pistons to start with, you may struggle since new standard pistons aren’t currently available off-the-shelf, and new-old stock sets are scarce.

1There are more problems too, since the piston crown

heights are completely different; therefore, the standard 1500 piston sits 5 mm down the bore and since this needs to correspond to a combustion chamber in the head, the effect is very low compression.

That drop in piston height equates to a 30 cc increase in combustion chamber (including the head gasket thickness), which can be corrected to up a point by decking the block and the cylinder head to restore volume to anything approaching standard compression ratio (CR). That’s OK but you can already see there’s a compromise since we’re now being dictated by the CR rather than tailoring it to our

needs — there’s effectively less CR for us to play with...

In truth, Joe reports that you would actually need to deck the block anyway since it more than likely needs cleaning up. But with this method you take off far more than is normally necessary, which effectively means you could be compromising the integrity of the block — especially if you go too far. 3-4 mm won’t case a problem, but 5 mm is risky with many blocks.

2One of the solutions is to use an aftermarket piston.

Several are available from the more common suppliers although Joe has the option of speccing his own using CP forged pistons. This may sound like an expensive route, but it isn’t as prohibitive as you might think. “We can supply any bore size you like — up to 86 mm is possible with a Pre-Crossflow head — with any crown height and all for the same money,” reckons Joe. Expect to pay around £520 a set.

In this case, a crown height of 44.5 mm brings the piston flush with top of the 711M Crossflow

block, but there is a better way if you’re in the market for alternative con-rods.

3 They’re scarce in standard form, but the BDA uses a

longer rod than standard Crossflow at 5.23 inch as opposed to 4.92 inch. That might not sound a lot, but the result is a considerably lighter piston and better rod angle giving a free-revving engine and broader torque curve.

You aren’t likely to come across a set of BDA rods that easily — although they do come up. The more common method is to use aftermarket, forged rods of this length, coupled with a crown height of 37.2 mm, giving you long rods and a piston height level with the 711M top face (a slightly shorter piston is usually needed to allow for block refacing).

Couple this with an 83.5 mm bore and you’ll get the desired 1700cc, all on a standard Crossflow block that’s not particularly strained in

comparison to a Pre-Crossflow.

hybrid pre-crossflows

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ROD AND PISTON COMBINATIONS

Aftermarlet longer con-rods allow shorter (lighter) pistons and a better rod angle.

Most Crossflow engines have the combsution chamber in the piston (left), making it heavy compared to the Pre-Crossflow’s flat-top type.

Unlike the Pre-Crossflow engine, almost all Crossflows feature flat-face cylinder heads.

Forged pistons aren’t cheap, but they are readily available do allow you to specify your desired bore size.

This hybrid Pre-Crossflow features a 1700 Crossflow bottom end, but it’s all period on top with Aquaplane goodies. The enjgine’s destined for a 100E Escort estate belonging to Darren Preston.

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Left to right: 5.23 inch BDA con-rod, 4.92 inch 1600 Crossflow rod, 4.8 inch 1500/Lotus twin-cam rod, 1300 Crossflow rod, and Anglia 997 rod.

You can use any rear-drive 1600 Crossflow block, but the more-common 711M version is best.

Below: just to confuse matters, early Crossflow engines had a small combustion chamber in the head, too.

hybrid pre-crossflows

Cylinder Heads

Cams and performance potential

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1300 CROSSFLOW BLOCKS711M Crossflows aren’t restricted to 1600cc, hence you can use a 1300 Crossflow block in place of a 1200 Pre-Crossflow block, or indeed, there is a (fairly scarce) 1300cc Pre-Crossflow block too, and they’re all the same height. Joe reports that, with the combination of 1100 Crossflow rods, a 1300 crank and Pre-Crossflow-height pistons, coupled with an A6 cam and 40 DCOEs, you can achieve 110 bhp with 1500-size valves in an Anglia head casting. Like the 1600/1700 versions, you can go even further using bespoke pistons and forged rods — upwards of 130 bhp in full-race trim. The 1300 is a very underrated engine in Joe’s opinion with loads of revvy potential.

There are more advantages to using virtually bespoke pistons and aftermarket rods because, as we hinted at earlier, you aren’t compromised by trying to restore the CR back to a decent level. By comparison, you can now dictate what level you want. “For most road engines running pump fuel we’d aim for around 10.5:1, depending on the cam,” comments Joe.

The preferred head is the 1500GT, which we’ve covered before and in this instance you’d need a chamber of around 39cc to achieve the aforementioned CR using a 1700 bottom end. By contrast, if you used a 1500 block configuration, you’d need a

combustion chamber of 34cc to achieve the same level.

This means you can optimise the cylinder head even further since, by allowing us to increase the size of the combustion chamber to achieve a CR of 10.5:1 (or higher if required) we can now de-shroud the valves further,or even use larger valves. This has always has been a problem with these Pre-Crossflow heads — flow always has been a compromise balanced between flow and the compression ratio needed. So not only will you achieve greater capacity, you will also achieve better flow and ultimately more performance.

When you build top-spec Pre-Crossflows for the road and track, it’s a nice idea to have a demonstrator to show how good they can be, which is the point of Joe’s Mk1 Cortina. He races a Willment replica Mk1 GT but it isn’t road legal, meaning you can hardly go round the block in it. This one, however, is an unrestored, rot-free two door, complete with Joe’s steering products and ideas, plus a 1700, 711M-blocked engine with Throbnozzle head, A6 cam and twin 40 DCOEs. As you can imagine it goes like a greased rocket, handles as it should and stops too. With 140 bhp on tap it’s one demonstrator we’d queue up to drive...

STRICTLY STREET JOE’S ROAD-READY MK1

“IF YOU WANT TO GO BEYOND 1700, YOU CAN WITH THE BIGGER-CAPACITY AX BLOCK”

Using a bigger-capacity bottom end means you can have bigger combustion chambers and larger valves.

1500GT head is the best one to use as a starting point. This one’s being optimised for a 1700 build.

Thicker AX Crossflow blocks allow capacities of 1800cc and upwards.

This flow graph shows one of Joe’s 31cc 1500 full-race heads (red line) versus a 33.5cc head for a 1700 (blue line). As you can see, the extra few cc he is able to remove from the chamber plus a slightly bigger valve make a difference.

Pre-Crossflow in Joe’s road Mk1 features a 1700 Crossflow bottom end, but still looks perfectly-period.

An A6-grind cam is a great all-rounder when combined with a decent head and twon 40 DCOEs.

Early Mk1 two-door Cortina is Joe’s current ‘demonstrator’. A left-hand-drive import, the sleeper exterior is hiding upgraded suspension, brakes and, of course, a hybrid Pre-Crossflow.

There are a massive range of cams available for the whole Kent range. You may have your favorites and Joe does, too. He reports that, coupled with a pair of 40 DCOEs, an A6 cam is one of the best all-round performing components you can fit.

Other components you will need are a properly ported head with combustion chambers to suit a 1700. Coupled with 39.6 mm and 33.7 mm valves, you could see around 140 bhp from a long-rod 711M-block Pre Crossflow.

There is more power potential available — Joe’s own race car

(when competing in the CTCRC series) can run a 711M bottom end, and in this guise it can produce 150 bhp with a similar spec engine albeit with an A8+ cam, and over 160 bhp plus 132 lb.ft of torque with a bespoke Throbnozzle cam, narrow-stem race valves and 45 DCOEs.

If you want to go beyond this, you can with a greater-capacity AX block, which was meant to bore to a configuration of 1800cc, but will go way beyond since it has a far thicker cylinder wall, although Pre-Crossflow heads won’t generally tolerate any more than an 86 mm bore.